Deeply Rechargeable Battery Systems and Methods
Deeply rechargeable battery systems and methods, where a core/shell nanoscale structure provides deeply rechargeable anodes that overcome intrinsic limitations of conventional battery materials that involve soluble intermediates or insulating discharge products. The deeply rechargeable battery systems and methods simultaneously overcome the dilemmas of passivation and dissolution. An ion-sieving concept is applied to a Zn anode that confines larger zincate ions and allows smaller hydroxide ions to permeate, can limit/prevent ZnO dissolution and electrode shape change.
This application claims the benefit of U.S. Provisional Patent Application No. 62/895,455 filed 3 Sep. 2019, the entire contents and substance of which are hereby incorporated by reference as if fully set forth below.
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BACKGROUND OF THE DISCLOSURE 1. Field of the DisclosureThe various exemplary embodiments of the disclosure relate generally to processes, methods, and systems energy carrying. It is particularly related to deeply rechargeable battery systems and methods.
2. BackgroundAlternative energy carriers have been sought after due to fossil fuels' slow regeneration and environmental concerns such as climate change, air and water pollution. Indeed, the depletion of fossil fuel resources is leading to steadily increasing energy demands.
Sustainable electrochemical energy storage (EES) systems are being sought that are low-cost, reliable, and eco-friendly. Extensive research into EES in recent years has prompted the emergence of technologies for applications in portable devices, electric vehicles (EVs) and grid-scale energy-storage systems.
When carrying clean electricity from solar or wind, batteries are promising to alleviate the current energy and environmental problems. A wide variety of electrochemical cells, or “batteries,” are known, and in general are devices that convert chemical energy into electrical energy by means of an electrochemical oxidation-reduction reaction.
Batteries can be generally described as comprising three components: an anode that contains a material that is oxidized (yields electrons) during discharge of the battery (i.e., while it is providing power), a cathode that contains a material that is reduced (accepts electrons) during discharge of the battery, and an electrolyte that provides for transfer of ions between the cathode and anode. During discharge, the anode is the negative pole of the battery, and the cathode is the positive pole.
Batteries can also be generally categorized as being “primary,” where the electrochemical reaction is essentially irreversible, so that the battery becomes unusable once discharged, and “secondary,” where the electrochemical reaction is, at least in part, reversible so that the battery can be “recharged” and used more than once. Secondary batteries are increasingly used in many applications because of their convenience (particularly in applications where replacing batteries can be difficult), reduced cost (by reducing the need for replacement), and environmental benefits (by reducing the waste from battery disposal).
Secondary batteries utilizing faradaic energy storage mechanisms are the most prominent systems among the EES technologies. Undoubtedly, lithium-ion batteries (LIBs) have been an enormous success in the realms of portable devices and EVs due to their high energy density, light weight, and low self-discharge rate. For these reasons, LIBs are still receiving significant attention.
However, LIBs continue to face challenges related to safety (with their use of flammable organic electrolytes), energy density, longevity, and concerns around material availability (such as Li and Co metals). Particularly, battery safety is an increasingly vital concern in electric vehicle applications. These issues seriously limit the popularization of EVs and the development of grid-energy storage.
One approach to these limitations includes research into fluorinated organic electrolytes and solid-state electrolytes as alternatives to flammable organic solvents. Another approach towards ultra-safe batteries is to develop battery chemistries that are compatible with aqueous electrolytes. Batteries that use aqueous electrolytes have enhanced safety, ion conductivity, and cost-effectiveness. Yet, a main obstacle to successful aqueous batteries includes their narrow stable voltage window and evolution of hydrogen and oxygen gases that occurs upon the electrolysis of water.
Neutral and alkaline electrolytes are two major classes of aqueous electrolytes for zinc anodes. Rechargeable zinc anodes in neutral electrolytes such as “water-in-salt” electrolytes and molten hydrate electrolytes have been investigated. Nonetheless, cycling zinc anodes deeply in alkaline electrolytes remains challenging due to the dramatic change of the chemical and physical forms of zinc species and the severe hydrogen evolution side reaction during cycling. Despite the challenges, it is important to enable highly rechargeable zinc anodes in alkaline electrolytes to propel the development of rechargeable Zn-air batteries, as air cathodes kinetically favor alkaline electrolytes over neutral ones.
Although non-alkaline electrolytes have been investigated for Zn-air batteries, their oxygen reduction reaction (ORR) and their oxygen evolution reaction (OER) kinetics at the air cathode are slow. In alkaline electrolytes, there are two consecutive zinc conversion reactions (Complexation, Equation (1) and Anode, Equation (2)). This solid-solute-solid mechanism inherently causes passivation and dissolution issues on zinc anodes.
ZnO+H2O+2OH−Zn(OH)42− (1)
Zn(OH)42−+2e−Zn+4OH− (2)
These issues are due to the following processes: (i) the insulating discharge product ZnO passivates the surface of zinc anodes, preventing the latter from further discharging or recharging back to metallic zinc, and (ii) the intermediate zincate Zn(OH)42− is soluble in alkaline electrolytes, which leads to active material loss, random ZnO precipitation on the electrode, and morphology change of the electrode over cycling.
In addition, the hydrogen evolution reaction (HER) Equation (3) is a side reaction on the zinc anode. In an alkaline electrolyte with pH 14, the Zn/ZnO standard reduction potential (−1.26 V vs the standard hydrogen electrode (SHE)) is lower than that of the HER (−0.83 V vs SHE). Thus, HER is thermodynamically favored during charging, which causes low Coulombic efficiency, electrolyte drying, bubble accumulation, and eventually cell failure.
2H2O+2e−H2+2OH− (3)
A battery-gas chromatography (GC) quantitative analysis method is used herein to identify the influence of HER on the capacity loss of zinc anodes. The cathode and overall reactions are, respectively:
2ZiOOH+2H2O+2e−2Ni(OH)2+2OH− (4)
2ZiOOH+Zn+H2O2Ni(OH)2+Zn (5)
In consideration of Zn anodes, HER suppressing Zn anodes should possess high Coulombic efficiency (discharge capacity/charge capacity). Thus, the need for ultra-safe, high-energy, and low-cost EES devices has prompted a search for new energy-storage technologies.
Within the stability window of water, zinc is an attractive anode material because it is the most active metal that is stable with water. Rechargeable Zn-based aqueous batteries have immense potential in large-scale energy storage systems due to their high gravimetric capacity (specific capacity) of 820 milliampere hours per gram (mA·h/g; hereinafter “mAh/g” or similar units) and high volumetric capacity of 5854 milliampere hours per cubic centimeter (mA·h/cm3; hereinafter “mAh/cm3”, “mAh/mL” or similar units), cost effectiveness, and high chemical stability in air and aqueous solution. Thus, as an anode, Zn has roughly three times the volumetric capacity compared to Li (2062 mAh/cm3). Without the necessity of flammable organic electrolyte, aqueous Zn-based batteries do not require the comparably complex subsystems required for lithium-based batteries including thermal management, sophisticated electronic controls, and structural protection to manage any catastrophic events.
By using aqueous electrolyte, zinc-based batteries not only are safer, but also can be manufactured in ambient air rather than dry room, and have much higher tolerance to moisture and air during operation. Having two valence electrons and high density, zinc metal has three times the volumetric capacity of lithium metal. Among various zinc-based batteries, Zn-air has a theoretical volumetric energy density (energy density) of 4400 watt-hour per liter (W·h/L; hereinafter “Wh/L” or similar units), that is more than three times of conventional Li-ion batteries (1400 Wh/L), and approaching Li-S batteries (5200 Wh/L). Primary Zn-air batteries have already been the battery of choice for hearing aids, which require extremely high energy density and safety. Finally, zinc is abundant, low-cost, and environmentally benign, rendering them suitable for large scale applications.
In contrast to a LIB graphite host anode, which undergoes intercalation and de-intercalation, the zinc anode undergoes dissolution/precipitation, complexation, and reduction/oxidation repetitive processes during the charge/discharge process in aqueous electrolytes. The overall reactions on the zinc anode are:
As a result of this dissolution/precipitation cycle, the longstanding constraint that has prevented the implementation of Zn in next-generation batteries for large-scale application is its poor rechargeability due to, among other things, dendrite growth, shape change, and passivation.
Major challenges for a rechargeable Zn anode for aqueous batteries as a result of the solid-solute-solid mechanism, the insulating nature of discharge product (ZnO), and the water stability window include: (1) ZnO (the soluble and insulating discharge product) passivates the surface of unreacted Zn, which leads to low utilization of active material and a poor rechargeability; (2) ZnO dissolution causes Zn deposition to happen in random locations, which leads to electrode morphology change and dendrite growth after continuous cycling. In a lean electrolyte configuration, the Zn dendrite can penetrate the separator to short-circuit the battery; and (3) H2 evolution on the Zn anode compromises Coulombic efficiency. Especially in a sealed cell with a limited amount of electrolyte (rather than the often-used beaker cell with saturated ZnO), H2 evolution dries out the electrolyte, enhances internal pressure of the battery, and gas bubbles block the ionic pathway, which leads to a low Coulombic efficiency (≈60%) and even sudden battery failure.
Zn dendrites are formed during the charging process (i.e., electrodeposition of Zn metal) when Zn(OH)42− and/or Zn2+ ions are deposited unevenly, with faster growth occurring along energetically favorable crystallographic directions, resulting in internal short circuit. Furthermore, incomplete reduction of zincate ions coupled with non-uniform redistribution of Zn electrode material during the charging process leads to densification of the electrode at specific regions over many charge/discharge cycles, causing loss of usable capacity.
Aside from dendrite formation and shape change of the Zn electrode, the passivation layer on the bulk zinc anode shortens the cycle life because active Zn is transformed into relatively insulating ZnO, which increases the internal resistance of the Zn electrode. This passivation inhibits the discharge process as the insulating ZnO film on the Zn surface blocks the migration of the discharge products and/or hydroxide ions, causing significant loss of energy efficiency for the charge/discharge cycles. While the passivation mechanism of the Zn anode in alkali electrolytes has been investigated, effective methods for resolving this problem have yet to be proposed.
Attempts have been made in the past to overcome one or two of the challenges of passivation, dissolution, and HER. For example, a recent attempt has been made to mitigate dendrite formation and shape change of the Zn electrode by altering the Zn electrode design. In one, a 3D-zinc sponge anode was prepared to improve the rechargeability of Zn-based batteries. Although the performance of the zinc battery improved with this design, problems persist: (1) passivation is still present in the 3D-zinc anodes, especially with a high depth of discharge (DOD); (2) the larger electrode-electrolyte contact area accelerates the dissolution of zinc, leading to shape change and capacity fading; and (3) the volume capacity decreases because of the porosity of the zinc sponge and the low depth-of-discharge.
In another investigation, Zn anodes with a carbon coating were utilized to improve anti-corrosion performance. However, most of these studies could not overcome the dissolution and passivation problems simultaneously. In these studies, although nanoscale, carbon-coated zinc oxide particles were used as anode materials in rechargeable zinc cells, there is considerable room for improvement to mitigate the dissolution problem. An anode composed of micron-sized ZnO spheres was synthesized by a complicated co-precipitation process or ball milling approach, which increased the tap density of the electrode, but the passivation problem still needs to be resolved.
Also, some zinc battery systems using mild electrolytes, such as ZnSO4-MSO4 (M=Mn, Co), Zn(CF3SO3)2—Mn(CF3SO3), and Zn(TFSI)2—LiTFSI, in which expensive TFSI salts should be replaced with salts having lower costs, were developed to mitigate the zinc dendritic growth effectively. Nevertheless, the reversibility of a zinc anode in alkaline electrolyte is a great concern to exploit some highly rechargeable Zn-air batteries with high specific energy density (5200 Wh/kg).
In terms of battery testing protocols, most previous results of Zn anode performance were obtained using beaker cells rather than closed cells (cylindrical cells or coin cells). In these beaker cells, abundant electrolyte significantly decreased the overall specific capacity of batteries. Also, since electrolyte saturated with ZnO was used in these beaker cells, it is difficult to ascribe the contribution of active material and calculate the performance of batteries due to the inevitable reduction of zin-cate from outsourcing of ZnO in the electrolyte. The performance of these cells cannot reflect real conditions in practical commercial batteries in which the reasonable electrolyte content is a pivotal factor for high volumetric and gravimetric capacity.
These problematic conventional battery testing protocols raise several problems: (1) the amount of electrolyte exceeds the amount of electrode materials by ≈1000 times, which lowers the overall energy density and covers the problem of electrolyte side reactions; (2) the open cell configuration covers the problem of gas evolution and cell swelling; (3) the electrolyte is usually saturated with ZnO to extend the cycle life. Yet, the capacity from the ZnO dissolved in the electrolyte is 250-fold the active material used (for example, assuming 10 mL of electrolyte and ZnO solubility of approximately 0.256 mol/L measured by inductively coupled plasma), and the mass of dissolved ZnO is not counted when calculating the specific capacity. The true performance of the active material was not evaluated; (4) the utilization of Zn is usually low (<approximately 50%), which extends the cycle life, but lowers the overall energy density.
As noted, advantages of the Zn-air cell compared to the Li—S cell are that Zn is much more economical than Li and the battery is safer due to absence of flammable organic liquid, making Zn-based batteries attractive candidates for electric vehicles and large-scale energy storage. There has been recent progress on rechargeable Zn anode materials in neutral or mildly acidic conditions that eliminate concerns of ZnO passivating the Zn surface.
In order for Zn-based aqueous batteries to have higher specific energy than state-of-the-art LIBs, however, an oxygen cathode must be used, which favors alkaline electrolytes (e.g., KOH) to facilitate the ORR and the OER. Although developing efficient ORR and OER electrocatalysts could lower the polarization and improve the round trip energy efficiency of Zn-air batteries, their reversibility is mainly limited by the Zn anode, which has received far less attention.
From the above, it is evident that improvements in battery technologies are needed. Batteries can be characterized by the specific materials that make up each of the three main components of the anode, cathode and electrolyte. Selection of these components can yield batteries having specific voltage and discharge characteristics that can be optimized for particular applications.
Although stable cycling of Zn anodes in mild acidic electrolyte has been demonstrated, an alkaline electrolyte is ideal for zinc-air batteries because an oxygen cathode has minimum overpotential in alkaline electrolyte. However, a deeply rechargeable (>50% DOD) Zn anode in lean alkaline electrolyte (mass ratio of electrolyte to electrode <100:1) is still lacking due to multiple challenges.
A particularly rich avenue for increased benefits relates to improvements in rechargeability and specific capacities by limiting passivation and dissolution issues related to the choices of anode, cathode and electrolyte. While Zn vs. Li is discussed above, various chemistries can provide the improvements being sought. An exemplary electrode would include anodic core elements comprising core material, the core material having a passivation interface size and an intrinsic dissolution rate, and a conformal shell coating on an outer surface of the anodic core elements forming core/shell structures, wherein the anodic core elements comprise a feature size smaller than the core material passivation interface size, and wherein a dissolution rate of the core material from the core/shell structures is less than the intrinsic dissolution rate. Further, the shell should be made of material that has low activity towards the HER of reduction of water to hydrogen as a side reaction.
BRIEF SUMMARY OF THE DISCLOSUREIn exemplary embodiments of the present invention, core/shell nanoscale structures provide deeply rechargeable anodes, and can overcome intrinsic limitations of other battery materials that involve soluble intermediates or insulating discharge products.
Starting with a nanomaterial with high-surface area could avoid the passivation layer problem. However, the dissolution problem is more severe. On the other hand, a nonporous coating could prevent ZnO dissolution, but would also block the OH− transport necessary for the zinc redox reaction to occur. Therefore, simultaneously solving the dilemmas of passivation and dissolution are an answer.
While specific exemplary embodiments disclose particular metals, coatings, thicknesses, the present invention encompasses a myriad of core material/coatings that with optimization of the core and shell materials, from aspects of pore size, porosity, and surface charge, leads to various improvements of anode performance and stability. Many materials with controlled ion-sieving and HER suppressing properties are contemplated herein. The design principles can be applied to other morphologies (e.g. particles) of starting materials for large scale production. The mechanistic understanding and design principles cover many types of rechargeable high-energy aqueous batteries.
The concept of separating ions and molecules by size using selective membranes is known. A variety of materials such as graphene, graphene oxide, polymer, and metal carbide membranes with a controllable pore size and permeability have been demonstrated to have ion-sieving capabilities in various applications. Applying the ion-sieving concept to Zn anode, to confine larger zincate ions and allow smaller hydroxide ions to permeate, can limit/prevent ZnO dissolution and electrode shape change.
In an exemplary embodiment of the present invention, an electrode comprises anodic core elements comprising a core material of zinc, the core material having a core material passivation interface size of approximately 2 μm, a core material intrinsic dissolution rate, and a core material hydrogen evolution reaction (HER) rate.
The electrode further comprises a conformal shell coating of TiO2 on an outer surface of the anodic core elements, thus forming ZnO@TiO2 core/shell structures. The electrode can be a sub-micron zinc anode sealed with an ion-sieving coating that suppresses hydrogen evolution reaction. ZnO nanorods are coated with TiO2, which overcomes passivation, dissolution, and hydrogen evolution issues simultaneously. It achieves superior reversible deep cycling performance with a high discharge capacity of approximately 616 mAh/g and Coulombic efficiency of approximately 93.5% when cycled with 100% depth of discharge at lean electrolyte. It can also deeply cycle ˜350 times in a beaker cell.
In an exemplary embodiment, the electrode further comprises a conformal shell coating of TiNxOy on an outer surface of the anodic core elements, thus forming ZnO@TiNxOy core/shell structures. The anodic core elements are nanoscale, so as to comprise a feature size smaller than the zinc passivation interface size. The anodic core elements can be nanorods with a diameter of less than approximately 2 μm, and more preferably less than approximately 500 nm.
The dissolution rate of zinc from the core/shell structures is less than the Zn intrinsic dissolution rate, as the relatively thin (having a thickness of less than approximately 10 nm) and conformal TiNxOy coating mitigates Zn dissolution in an alkaline electrolyte.
The ZnO@TiNxOy core/shell nanorod structures provide a deeply rechargeable Zn anode. The small diameter of ZnO limits to fully prevents passivation, and allows near to full utilization of active materials, while the relatively thin and conformal TiNxOy coating not only mitigates the Zn dissolution, but also mechanically maintains the morphology of the nanostructures, and delivers electrons to the nanorods. As a result, the ZnO@TiNxOy core/shell nanorod anode achieves superior specific capacity and cycle life compared with bulk Zn foil and uncoated ZnO nanorod anodes.
The discharge capacity of the ZnO@TiNxOy core/shell nanorod anode is approximately twice as large as that of an uncoated ZnO nanorod anode. It was surprisingly found that the ZnO@TiNxOy nanorod anode achieves a much higher specific discharge capacity of approximately 508 mAh/g than that of conventional zinc anodes. Further, it can deeply cycle greater than approximately 640 times (over 64 days) in a beaker cell, and can deliver excellent long-term electrochemical performance (more than approximately 7500 cycles) when cycled under start-stop conditions.
In another exemplary embodiment of the present invention, an electrode comprises anodic core primary elements comprising a core material of zinc, the core material having a core material passivation interface size of approximately 2 μm, a core material intrinsic dissolution rate, and a core material HER rate.
The electrode further comprises a conformal shell coating of carbon on an outer surface of the anodic core primary elements, thus forming ZnO@C core/shell structures. The anodic core primary elements are nanoscale, so as to comprise a feature size smaller than the zinc passivation interface size. The anodic core primary elements can be particles with a diameter of less than approximately 2 μm, and more preferably are nanoparticles (NPs) with a diameter of less than approximately 100 nm.
The dissolution rate of zinc from the core/shell structures is less than the Zn intrinsic dissolution rate, as the relatively thin (having a thickness of less than approximately 15 nm) and conformal amorphous, microporous, and conductive carbon coating mitigates Zn dissolution in an alkaline electrolyte.
An assembly (secondary cluster) of these core/shell structures form Zn-pome microspheres (pomegranate-like nanoporous carbon-coated ZnO clusters). Each secondary cluster/Zn-pome microsphere can be approximately 6 mm in size and comprise on the order of approximately 105 ZnO NPs individually encapsulated by an amorphous, microporous, and conductive carbon shell that slows down the dissolution of zincate intermediate species during cycling. The shell further suppresses zinc dissolution by decreasing the electrode-electrolyte contact area.
The nanoscale, pomegranate-structured Zn anode can be fabricated via a bottom-up microemulsion approach. As disclosed, the in the Zn-pome, primary ZnO NPs assemble into secondary clusters after which they are individually encapsulated by a conductive, microporous carbon framework. The small size of ZnO NPs overcomes the problematic issue of passivation, whereas the secondary structure and ion-sieving carbon shell mitigates the dissolution problem.
Inductively coupled plasma (ICP) analysis confirms that Zn dissolution from the Zn-pome anode is effectively suppressed, leading to a considerably prolonged cycle life compared to that of a conventional ZnO anode in an alkaline aqueous electrolyte. The Zn-pome anode maintains its capacity after long resting. This performance is achieved in harsh yet practical conditions: a limited amount of electrolyte, sealed coin cells, and approximately 100% DOD.
In another exemplary embodiment of the present invention, an electrode comprises anodic core primary elements comprising a core material of zinc, the core material having a core material passivation interface size of approximately 2 μm, a core material intrinsic dissolution rate, and a core material HER rate.
The electrode further comprises a conformal shell coating of an ion-sieving carbon on an outer surface of the anodic core elements, thus forming ZnO@C core/shell structures. The anodic core primary elements are nanoscale, so as to comprise a feature size smaller than the zinc passivation interface size. The anodic core primary elements can be particles with a diameter of less than approximately 2 μm, and more preferably are nanoparticles (NPs) with a diameter of less than approximately 100 nm.
The dissolution rate of zinc from the core/shell structures is less than the Zn intrinsic dissolution rate, as the relatively thin (having a thickness of less than approximately 30 nm) and conformal ion-sieving carbon coating mitigates Zn dissolution in an alkaline electrolyte.
The ion-sieving carbon nanoshell coated ZnO nanoparticle anode can be synthesized in a scalable way with controllable shell thickness. The nanosized ZnO prevents passivation, while the microporous carbon shell slows down Zn species dissolution. Under extremely harsh testing conditions (closed cell, lean electrolyte, no ZnO saturation), this Zn anode shows significantly improved performance compared to Zn foil and bare ZnO nanoparticles. The ion-sieving nanoshell can be beneficial to other electrodes such as sulfur cathode for Li-S batteries.
In another exemplary embodiment of the present invention, an electrode comprises anodic core elements comprising core material, the core material having a core material passivation interface size, a core material intrinsic dissolution rate, and a core material hydrogen evolution reaction (HER) rate, a conformal shell coating on an outer surface of the anodic core elements forming core/shell structures, wherein the anodic core elements comprise a feature size smaller than the core material passivation interface size, wherein a dissolution rate of the core material from the core/shell structures is less than the core material intrinsic dissolution rate; and wherein the HER rate of the shell is less than the core material HER rate.
The electrode can be deeply rechargeable.
The electrode can have a DOD of greater than 50%.
The core material can be selected from the group comprising a metal, metal oxide, metal sulfide, and combinations thereof.
The core material can be selected from the group comprising Zn, Li, Na, Mg, Ca, ZnO, Li2O, Na2O, MgO, CaO, ZnS, Li2S, Na2S, MgS, CaS, and combinations thereof.
The conformal shell coating can comprise a cermet. The conformal shell coating can comprise carbon.
The core/shell structures can have a specific discharge capacity of at least 70% of the theoretical limit of the specific discharge capacity of the core material.
The electrode can have a coulombic efficiency greater than about 93.5%.
The anodic core/shell structures can be formed by a deposition technique of layers of the conformal shell coating over a deposition cycling series, and wherein a morphology of the anodic core elements prior to the deposition cycling series is substantially the same as a morphology of the core/shell structures after the deposition cycling series.
The anodic core/shell structures can be formed by an atomic layer deposition (ALD) technique of layers of the conformal shell coating over an ALD cycling series, and wherein a morphology of the anodic core elements prior to the ALD cycling series is substantially the same as a morphology of the core/shell structures after the ALD cycling series.
In another exemplary embodiment of the present invention, the anodic core elements are nanorod structures, the core material comprises ZnO, and the conformal shell coating comprises TiNxOy.
The diameter of the nanorods can be less than approximately 2 μm. The diameter of the nanorods can be less than approximately 500 nm.
The conformal shell coating can have a thickness of less than 10 nm. The conformal shell coating can have a thickness of less than approximately 6 nm.
In another exemplary embodiment of the present invention, the anodic core elements are nanoparticles, the core material comprises ZnO, and the conformal shell coating comprises carbon.
The conformal shell coating can comprise an amorphous, microporous, and conductive carbon.
An assembly of core/shell structures can form Zn-pome microspheres (pomegranate-like nanoporous carbon-coated ZnO clusters). Each Zn-pome microsphere can have a diameter of approximately 6 μm. Each Zn-pome microsphere can comprise on the order of approximately 105 core/shell structures.
The diameter of the nanoparticles can be less than approximately 2 μm. The diameter of the nanoparticles can be less than approximately 100 nm.
The conformal shell coating can have a thickness of less than 15 nm. The conformal shell coating can have a thickness of less than approximately 10 nm.
In another exemplary embodiment of the present invention, the anodic core elements are nanoparticles, the core material comprises ZnO, and the conformal shell coating comprises an ion-sieving carbon shell.
In another exemplary embodiment of the present invention, a rechargeable battery system comprises anodic core/shell structures comprising a ZnO core coated with a shell layer of TiNxOy, an aqueous electrolyte, and a cathode.
In another exemplary embodiment of the present invention, a rechargeable battery system comprises anodic Zn-pome microspheres each comprising a pomegranate-like assembly of individual ZnO nanoparticles coated with a shell layer of carbon, an aqueous electrolyte, and a cathode.
In another exemplary embodiment of the present invention, a rechargeable battery system comprises anodic core/shell nanoparticles comprising a ZnO core coated with a shell layer of ion-sieving carbon, an aqueous electrolyte, and a cathode.
In each of the rechargeable battery systems, the rechargeable battery system can be deeply rechargeable.
In each of the rechargeable battery systems, the rechargeable battery system can have a DOD of greater than 50%.
In each of the rechargeable battery systems, the cathode can comprise Ni(OH)2.
In each of the rechargeable battery systems, the anodic core/shell structures can be formed by a deposition technique of the conformal shell on the core over a deposition cycling series, and wherein a morphology of the core prior to the deposition cycling series can remain substantially the same as the morphology of the core/shell structures after the deposition cycling series.
These and other objects, features and advantages of the present disclosure will become more apparent upon reading the following specification in conjunction with the accompanying description, claims and drawings.
The accompanying Figures, which are incorporated in and constitute a part of this specification, illustrate several aspects described below.
Although preferred exemplary embodiments of the disclosure are explained in detail, it is to be understood that other exemplary embodiments are contemplated. Accordingly, it is not intended that the disclosure is limited in its scope to the details of construction and arrangement of components set forth in the following description or illustrated in the drawings. The disclosure is capable of other exemplary embodiments and of being practiced or carried out in various ways. Also, in describing the preferred exemplary embodiments, specific terminology will be resorted to for the sake of clarity.
As used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise.
Also, in describing the preferred exemplary embodiments, terminology will be resorted to for the sake of clarity. It is intended that each term contemplates its broadest meaning as understood by those skilled in the art and includes all technical equivalents which operate in a similar manner to accomplish a similar purpose.
Ranges can be expressed herein as from “about” or “approximately” one particular value and/or to “about” or “approximately” another particular value. When such a range is expressed, another exemplary embodiment includes from the one particular value and/or to the other particular value.
Using “comprising” or “including” or like terms means that at least the named compound, element, particle, or method step is present in the composition or article or method, but does not exclude the presence of other compounds, materials, particles, method steps, even if the other such compounds, material, particles, method steps have the same function as what is named.
Mention of one or more method steps does not preclude the presence of additional method steps or intervening method steps between those steps expressly identified. Similarly, it is also to be understood that the mention of one or more components in a device or system does not preclude the presence of additional components or intervening components between those components expressly identified.
Exemplary embodiments of the present invention comprise innovative components of a deeply rechargeable battery system, and an innovative system and method of rechargeable batteries. A core/shell nanoscale structure provides deeply rechargeable anodes that overcome intrinsic limitations of conventional battery materials that involve soluble intermediates or insulating discharge products. The present invention simultaneously overcomes the dilemmas of passivation and dissolution. An ion-sieving concept is applied to a Zn anode that confines larger zincate ions and allows smaller hydroxide ions to permeate, can limit/prevent ZnO dissolution and electrode shape change.
Examples of the present invention include sealing ZnO nanorods for deeply rechargeable high-energy aqueous battery anodes, a deeply rechargeable zinc anode with pomegranate-inspired nanostructure for high-energy aqueous batteries, ion-sieving carbon nanoshells for deeply rechargeable Zn-based aqueous batteries, and a deeply rechargeable and hydrogen-evolution-suppressing zinc anode in alkaline aqueous electrolyte.
A Deeply Rechargeable and Hydrogen-Evolution-Suppressing Zinc Anode in Alkaline Aqueous ElectrolyteA GC quantitative analysis method (
The amount of NiOOH was in excess, which could guarantee the full depletion of Zn in the discharge step. In other words, the capacity loss (charge capacity-discharge capacity) on Zn anodes is attributed to side reactions on Zn anodes. As shown in
In an exemplary embodiment, the present invention comprises sealed sub-micron-sized anodes, coated with a HER suppressing ion-sieving layer to simultaneously tackle passivation, dissolution, and HER issues (
The critical thickness of ZnO passivation layer has previously been quantified to be 2 μm when a zinc metal anode is completely passivated. Thus, sub-micron-sized zinc anodes are believed to be able to overcome the passivation problem. However, decreasing the feature size to be nanoscale will intensify the dissolution and HER problems, due to increased electrode-electrolyte contact area. Therefore, sealing sub-micron-sized anodes by uniformly coating a HER suppressing ion-sieving layer is developed, which can suppress HER and selectively block larger zincate ions inside the coating while enabling OH−/H2O transport (
Coat technology is important, as conventional attempts with non-uniform coatings creates structures that still suffer dissolution and HER issues, which might be a reason these prior results had short cycle life (<20 cycles) and low specific discharge capacity. In this embodiment of the present invention, a TiO2 coating material is investigated to demonstrate it is stable with alkaline electrolytes and has a low HER activity.
The present HSSN anode was successfully fabricated as shown in
ZnO nanorods were grown on carbon papers (˜8.4 mg/cm2) by a hydrothermal method. Carbon paper (Fuel Cell Store) was first heated in air at 500° C. for 1 hour to increase its wettability. Then, the carbon paper was soaked in 0.1M KMnO4 (Sigma Aldrich) aqueous solution for 1 hour to form a seed layer. The ZnO precursor solution was prepared by mixing 50 mL zinc nitrate hexahydrate (30 mM, Alfa Aesar), 50 mL hexamethylenetetramine (30 mM, Sigma Aldrich), and ammonia (28.0-30.0% NH3 basis, Sigma Aldrich).
The seeded carbon paper was placed in the solution, followed by heating in an oven at 90° C. After DI-H2O washing and drying at 80° C. for 3 hours, the white-colored product on carbon paper was obtained. Different mass loadings (0.5˜5.5 mg/cm2) of ZnO nanorods on carbon paper were achieved by adjusting reaction conditions, as summarized in TABLE 1 and shown in
The HSSN zinc anode (a ZnO core/TiO2 shell structure) was synthesized using a solution method. The carbon paper with grown ZnO nanorods was immersed into a solution of 0.075M (NH4)2TiF6 and 0.2M H3BO3 for 10 minutes at room temperature. A layer of ˜30 nm thick TiO2 was deposited.
Synthesis of the ZnO@TiNxOy AnodeTo achieve the ZnO@TiNxOy anode, TiN was deposited onto the uncoated ZnO nanorod anode through ALD. ALD was conducted in Cambridge FIJI Plasma ALD system. The detailed ALD recipe is shown in
To measure the sheet resistance of TiNxOy and TiO2 coatings, TiNxOy and TiO2 are deposited onto glass slides, respectively. The glass slides were cleaned by sonication in acetone/ethanol, followed by ultraviolet-ozone (UVO) treatment. TiNxOy was obtained through an ALD of TiN on the glass slides followed by an oxidation step in air.
The precursors of TiN were TDMAT and N2. The detailed ALD recipe is shown in
The morphological and compositional analyses were carried out using SEM (Hitachi SU 8230), TEM (Hitachi HT7700, FEI Tecnai F30, and JEOL 100 CX-II), and STEM (Hitachi HD-2700). The XRD patterns (Panalytical XPert PRO Alpha-1) were carried out with Cu K-Alpha radiation. The XPS was measured with Thermo Scientific K-Alpha system. The specific BET surface areas and pore size distribution were determined by physisorption (BELSORP-max, MicrotracBEL Corp.). The dissolved Zn concentration of samples in 4M KOH electrolyte was measured with an ICP measurement. Cyclic voltammetry, linear sweep voltammetry, and electrochemical impedance spectroscopy were conducted using a VSP system (BioLogic). Battery cycling tests were carried out using LANHE operating in galvanostatic mode.
In the battery-gas chromatography quantitative analysis measurement, the airtight battery system (
The battery was charged at 20 mA for 15 minutes and then fully discharged (20 mA) to 0.8 V for 1 cycle. Then H2 measurements were conducted using the thermal conductivity detector. Ar was the carrier gas for gas chromatography. The capacity loss on the Zn anode is almost fully caused by HER (99.47%).
Capacity loss=Charge capacity−Discharge capacity=Capacity (HER)+Capacity (Other) (6)
The zinc anodes were cut to round disks with a diameter of 1 cm. Cathodes from commercial Ni—Zn AA batteries (PowerGenix), which is a mixture of NiOOH (˜8 mAh/cm2)/Ni(OH)2 (˜32 mAh/cm2), were harvested to pair with the anodes.
Coin CellCR2032 cases (MTI Corporation) were used to make coin cells. The aqueous electrolyte consists of 4M KOH (Sigma Aldrich, 99.99%), 2M KF (Alfa Aesar, 99.99%) and 2M K2CO3 (Alfa Aesar, 99.997%). 25 μL electrolyte was used. Glass fiber (GE Healthcare, Whatman™ 10370003) was used as the separator.
Pouch CellPouch-type batteries (
Cells are galvanostatically cycled at a charge rate of 1 C and a discharge rate of 5 C between 1.4 and 1.9 V. For anodes cycled at 100% DOD, the anodes were activated by being pre-cycled in pouch cells for 6 cycles. The charge capacity limit cut-off is 658 mAh/g (theoretical specific capacity of ZnO). For anodes cycled at 40% DOD, the anodes were activated by being pre-cycled with 100% active material utilization for 1 cycle and then being fully charged.
Beaker CellIn beaker-type batteries, the mass loading of active material (ZnO) on the anode is 1.6 mg/cm2. 10 mL ZnO-saturated 4M KOH (Sigma Aldrich) was used as the electrolyte. Cells are galvanostatically cycled at 100% DOD at a charge rate of 1 C and a discharge rate of 5 C between 1.4 and 1.9 V. The anodes were activated by being pre-cycled in beaker cells for 50 cycles. The charge capacity limit cut-off is 658 mAh/g. Ag wire was used as the anode terminal. Stainless steel wire was used as the cathode terminal.
As discussed, the charge capacity was limited to the theoretical capacity of ZnO (approximately 658 mAh/g). The theoretical specific capacity (charge capacity) was calculated by:
where MW is the molar weight of active material, n is the number of electrons transferred in the relevant reaction, and F is the Faraday's constant. In this work, MW of ZnO=81.38 g/mol; n=2; F=96485 C/mol.
The specific discharge capacity of the electrode was calculated by:
C=It/m (8)
where I is the discharge current, t is the discharge time per cycle, and m is active materials' mass (ZnO).
A rate of mC corresponds to a full charge/discharge in 1/m hour(s). The electrolyte-to-discharge-capacity (E/DC) ratio is:
E/C ratio=Volume of electrolyte/measured discharge capacity (9)
Thus, the theoretical gravimetric capacity of Zn metal is:
The theoretical volumetric capacity of Zn metal is:
Cν(mAh/cm3)=Cg*ρZn=5854 (11)
where ρZn is the density of Zn:
ρZn=7.14 g/cm3 (12)
The theoretical gravimetric energy density of Zn-air batteries (calculated based on the discharged state, ZnO) is:
where V is the battery voltage. V=1.66 V.
The theoretical volumetric energy density of Zn-air batteries is:
E84 (Wh/L)=Eg*ρZnO=6134 (14)
where ρZnO is the density of ZnO.
ρZnO=5.61 g/cm3 (15)
The TiO2 layer was coated on the ZnO nanorods via a mild solution method at room temperature. The ZnO nanorods were immersed in an aqueous solution comprising 0.075M (NH4)2TiF6 and 0.2M H3BO3. After the TiO2 coating, the ZnO nanorod structure was well maintained (
STEM image and elemental mappings (
During synthesis, (NH4)2TiF6 hydrolyzed to TiO2 on the surface of ZnO while the surface of ZnO slightly dissolved in the solution with acids produced by (NH4)2TiF6 hydrolysis. Thus, it appears some Zn species went into the TiO2 coating during the synthesis, which may explain for the Zn signal on the TiO2 shell.
As evidenced by
To evaluate the capability of the TiO2 shell to suppress zincate dissolution, both the HSSN and the uncoated ZnO anodes were soaked in a ZnO-free 4M KOH solution for 15 minutes. The ratio of ZnO active material mass and solution volume was 0.02 mg/μL. The dissolved Zn concentration was then measured in both solutions using inductively coupled plasma atomic emission spectroscopy (ICP-AES). As shown in
The zinc-based anodes were also characterized before and after a single charge in coin cells. As shown in
STEM images and elemental mappings of the present HSSN anode after charging are presented in
As discussed above, an ion-sieving coating layer is important for nanostructured Zn anodes to effectively suppress active material dissolution. In consideration of HER, such an ion-sieving coating layer should be HER suppressing. To evaluate the HER suppressing capability of the TiO2 shell and its effect on the Coulombic efficiency, HER activities of TiO2 and TiNxOy were investigated.
TiNxOy (
As shown in IR-corrected polarization curves (
TiO2 has lower electrical conductivity, which may be part of the reason for its lower HER activity and better HER suppressing capability. Simulations based on the force field model were also conducted to confirm the hydrogen suppressing property of TiO2. Cluster rather than the slab model was chosen because of its applicability in representing amorphous materials (
Simulation based on the force field model was conducted to investigate the hydrogen suppressing property of TiO2 and TiNxOy. The Monte Carlo and Least Squares techniques were used to minimize the energy. A Ti5O10 cluster was used to represent amorphous TiO2. For TiNxOy, the overall atomic ratio of O to N (O/N) was experimentally determined to be ˜6.66 as evidenced by XPS (
From many possible structures of amorphous TiNxOy, four representative models (denoted as TiNxOy-n, n=1, 2, 3, 4) were chosen and built with O/N atomic ratios of 9 and 4 to simulate the actual shell material. Ti5O9N cluster (O/N=9) for TiNxOy-1 and TiNxOy-2, and Ti5O8N2 cluster (O/N=4) for TiNxOy-3 and TiNxOy-4 were built. ΔGH* represents the free energy for H adsorption.
In a three-state diagram, comprising an initial H+ state, an intermediate H* state, and ½H2 as the final product, the material with higher |ΔGH*| value possesses lower catalytic activity and thus better hydrogen suppressing capability. ΔGH* was obtained by ΔGH*=ΔEH+ΔEZPE−TΔSH, where ΔEH is the binding energy of H species, and ΔEZPE and ΔSH are the zero point energy change and entropy change of adsorption H, respectively. The contribution of entropies and ZPE for AGH* were obtained, where finally ΔGH*=ΔEH+0.24 eV. ΔEH was obtained by ΔEH=EM−H−EM−½*EH
As shown in
The charge/discharge profiles of HSSN and ZnO@TiNxOy anodes cycled in lean electrolyte (100 μL) are plotted in
As shown in
The capacity fading occurs after 33 cycles. The battery failure can be attributed to (1) the structural collapse of the HSSN anode (
Voltage profiles for the batteries shown in
Electrolyte-to-discharge-capacity (E/DC) ratio is also critical for device-level energy density and is crucial for practical applications. The tested Coulombic efficiency of alkaline Zn anodes is highly correlated to the E/DC ratio. Thus, it is necessary to provide E/DC ratios to get a fair comparison on the Coulombic efficiency of different Zn anode materials. However, only a few previous works (summarized in the table of
Prior results were summarized, and the anode compared with them in terms of Coulombic efficiency and E/DC ratio in
In comparison, the present anode achieves a superior Coulombic efficiency (93.5%) at a low E/DC ratio (0.14 mL/mAh), which suggests the advance of the designed functionally coated Zn anodes (
The present zinc anode design, namely sealing sub-micron-sized ZnO with a HER suppressing and ion-sieving layer, to overcome simultaneously passivation, dissolution, and hydrogen evolution issues in alkaline electrolytes is disclosed. A ZnO nanorod anode and TiO2 shell were chosen to demonstrate this concept. The fabricated HSSN anode achieves superior reversible deep cycling performance at lean electrolyte. While the Coulombic efficiency of the present HSSN anode is higher than that of most of the previously reported zinc anodes, it will be improved to approach the efficiency of LIBs (99.9%).
Optimization of the shell material, from aspects of pore size, porosity, and surface charge, leads to improvement of anode performance and stability. Other materials with controlled ion-sieving and HER suppressing properties have the potential to be applied as the shell material. This design principle can potentially be applied to other morphologies (e.g. particles) of starting materials for large scale production. The mechanistic understanding and design principle herein will also guide future design of other rechargeable high-energy aqueous batteries.
Sealing ZnO Nanorods for Deeply Rechargeable High-Energy Aqueous Battery AnodesAs noted in the background, in aqueous alkaline electrolyte, a zinc anode undergoes two consecutive reactions: complexation (or dissolution) and electroreduction reactions in charging (shown in Equation 1: Complexation/Precipitation), and electrooxidation and precipitation reactions in discharging (shown in Equation 2: Electroreduction/Electrooxidation).
Different from conventional intercalation electrodes in lithium ion batteries, this solid-solute-solid (ZnO—Zn(OH)42−—Zn) transformation of zinc electrode inherently represents a series of challenges: (i) discharge product ZnO passivates the surface of Zn, preventing Zn from further discharging; (ii) ZnO is insulating, which can be hardly recharged to metallic Zn; and (iii) ZnO precipitation from soluble zincates occurs randomly on the electrode surface, and changes the morphology of electrode over cycling.
Zn metal foil is the most commonly used Zn anode in aqueous batteries. However, as exemplified in
As shown in
In an exemplary embodiment of the present invention as shown in
A hydro-thermal method was used to grow ZnO nanorods on carbon fiber paper. Then, the ALD technique was used to form a strong and conductive stable TiNxOy coating on the ZnO nanorods. This structure has advantages that include: (i) the feature size of each ZnO nanorod is smaller than the critical passivation size; (ii) a carbon paper framework and TiNxOy coating, which encapsulates the ZnO nanorod, function as an electrical pathway so that all ZnO nanorods are electrochemically active; and (iii) the TiNxOy coating enables fast hydroxide/water diffusion as well as blocks large zincates from escaping during electrochemical cycling, thus effectively preventing anode structure fracture.
Synthesis of ZnO NanorodsCarbon paper (Fuel Cell Store) was first heat-treated at 500° C. for 1 hour in air to increase its wettability. Then, ZnO nanorods were grown on the carbon paper by a wet chemical process. First, carbon paper was soaked in an aqueous solution containing 0.1M KMnO4 (Sigma Aldrich) for 1 hour to form a seed layer. Second, the seeded carbon paper was then dipped into a glass bottle with a precursor solution containing 50 mL zinc nitrate hexahydrate (30 mM, Alfa Aesar), 50 mL hexamethylene-tetramine (30 mM, Sigma Aldrich), and ammonia (28.0˜30.0% NH3 basis, Sigma Aldrich).
Third, the sealed bottle was placed into an oven at 90° C. Next, the white-colored carbon paper ZnO nanorods were obtained by water washing and drying at 80° C. for 3 hours. As shown in TABLE 2, different mass loadings of ZnO nanorods on carbon paper ranging from 0.5 mg/cm2 to 5.5 mg/cm2 were synthesized by adjusting: the carbon paper area per bottle, the NH3 concentration, the hydrothermal time, and the hydrothermal times.
The synthesis of ZnO@TiNxOy core/shell nanorods was conducted in Cambridge FIJI Plasma ALD system. First, the TiN was deposited onto the ZnO nanorods. The precursors of TiN were Tetrakis(dimethylamido)Titanium(IV) (TDMAT, Sigma Aldrich) and N2. During the TiN ALD process, the recipe was run 100 or 200 cycles at 250° C. The TiN ALD recipe is shown in
To investigate the Zn anode, full batteries were made using Ni(OH)2 as the rechargeable cathode. The Ni(OH)2 cathodes were harvested from commercial Ni—Zn AA batteries from PowerGenix.
Coin CellCoin-type batteries were assembled using CR2032 cases (MTI Corporation), the present zinc anodes (round disk, approximately 1 cm diameter) and Ni(OH)2 cathodes with excess capacity, as shown in
For start-stop operation, the ZnO@TiNxOy nanorod anode and Zn foil were pre-activated. The ZnO@TiNxOy nanorod anode was pre-cycled three times at 0.5 C between approximately 1.4 and 2 V. The Zn foil (approximately 0.02% DOD) was firstly discharged for 2 hours and re-charged for 2 hours at a constant current of approximately 1.35 mA. Then it was discharged twice and charged once at the same time interval of 1 hour at approximately 1.35 mA.
The Zn foil (approximately 1% DOD) was pre-cycled twice at a constant current of approximately 1 mA. When the Zn foil was used as the anode, the cathode harvested from commercial Ni—Zn AA batteries was electrochemically oxidized to approximately 0.6 V vs an HgO/Hg reference electrode in a beaker cell with 2M KOH as the electrolyte.
Pouch CellPouch-type batteries (
Beaker-type batteries (
EIS measurements were performed on a Bio-Logic instrument. The frequency range was between 100 KHz and 10 mHz. The amplitude of the AC signal was approximately 10 mV. Coin-type batteries assembled using the present zinc anodes and Ni(OH)2 cathodes were used to measure EIS. 100 μL 4M KOH, 2M KF and 2M K2CO3 electrolyte was added to a glass fiber separator.
Results and DiscussionZnO nanorods are synthesized on carbon paper with mass loading ranging from approximately 0.5 to approximately 5.5 mg/cm2 (
The nanorod morphology does not change after TiNxOy coating (
In addition to TEM, XPS results also indicate complete coverage of TiNXOy on ZnO (
The TiNxOy coating, although only a few nanometers thick, firmly supports the ZnO nanorod, blocks zincates, and enables OH−/H2O to pass through. As shown in
After 2 hours of charge (1 hour constant current at 1 C rate, and 1 hour constant voltage at 1.93 V), the uncoated ZnO nanorod anode shows severely morphological degradation, almost all ZnO nanorods detach from carbon paper because of dissolution (
EIS was also employed to investigate the electrochemical influence of conductive TiNxOy coating. As shown in the Nyquist plot (
Zinc anodes were tested in coin-type cells with lean zinc-free electrolyte here to evaluate their real performance (
The theoretical specific capacity of ZnO is approximately 658 mAh/g. As shown in
When testing zinc anodes in beaker cells with 10 mL ZnO saturated 4M KOH electrolyte, electrolyte can contribute a large capacity, which is 100 times that of in coin cells with 100 μL electrolyte (TABLE 3). With this big contribution, it is hard to evaluate the true performance of zinc anodes with less amount of active materials. Coin-type cells use minimum amount of electrolyte and have a higher volumetric capacity compared with beaker cells, which is a better testing choice even though the testing environment is harsh.
Moreover, it is hard to evaluate the true performance of anodes with a lot of capacity contributed from electrolyte. Coin-type cells use a minimum amount of electrolyte and have a higher volumetric capacity compared with beaker cells, which is closer to practical operating conditions. Thus, even though the coin cell with lean electrolyte is an extremely harsh testing environment (˜25 cycles), that was the choice made for this testing. To evaluate the true performance of anodes, ZnO-free electrolytes were used because capacity contributed by electrolytes could cause an unrealistically high capacity of anodes. 4M KOH, 2M KF and 2M K2CO3 was selected as the electrolyte if not otherwise stated because it has lower Zn(OH)42− solubility and thus less shape change than 4M KOH as evidenced by ICP results shown in TABLE 4.
ICP Emission Spectroscopy results below indicate that an electrolyte comprising 4M KOH, 2M KF and 2M K2CO3 has a lower Zn(OH)42− solubility than 4M KOH electrolyte.
As shown in
For the ZnO@TiNxOy anode, the TiNxOy coating did not change the over-potential of the ZnO anode with almost the same charge profile as the uncoated ZnO (
The superior performance of ZnO@TiNxOy nanorod anode can be attributed to the small feature size of ZnO and conformal TiNxOy coating. Below the critical passivation thickness, the anode passivation problem is nearly if not fully eliminated. The TiNxOy coating serves as an electrical pathway, confines large zincate molecules, yet allows OH− and water to pass. As a mechanical backbone, the TiNxOy coating protects ZnO nanorods from detaching from the carbon paper substrate, and thus provides a short zincate mass transfer path for the reaction.
Without a TiNxOy coating, the ZnO nanorod will detach from substrate upon charging (
The ZnO@TiNxOy nanorod anode was also tested in pouch cell with a ZnO-free electrolyte (
a: The cell structure and electrolyte quantity were not reported. It is assumed 10 mL electrolyte was used in beaker cells. Based on ICP result, the equivalent ZnO mass is approximately 208 mg.
b: Sandwich cell: anode, separator, and cathode were packed. The electrolyte quantity was not reported. It is assumed that the capacity contributed by ZnO saturated electrolyte was 2 times of that contributed by anodes.
c: Zinc in the electrode and electrolyte are both counted.
*: The mass loading was not reported. For calculation, it is assumed the mass of materials is 10 mg.
The ZnO@TiNxOy nanorod anode was also tested in a beaker cell (
In addition, the ZnO@TiNxOy nanorod anode has excellent performance under start-stop operations, demonstrating potential to replace lead acid batteries in micro-hybrid vehicles. Engine restart, rest and pulse discharge are involved in the start-stop operation. The procedure of a test is showed in
The ZnO@TiNxOy nanorod anode achieves very high specific discharge capacity and superior reversibility when testing in a coin cell with lean ZnO-free electrolyte. In commercial PowerGenix AA batteries, which are made of a Zn metal anode and NiOOH cathode, the discharge capacity decayed to approximately 50% of its initial capacity after only 9 cycles (0.5 C, 20° C., charged to approximately 105% theoretical capacity). NiOOH cathodes are very reversible, and the Zn anode is the main cause of the poor reversibility.
The present ZnO@TiNxOy core/shell nanorod anode structure successfully overcomes problems of ZnO passivation and zincate dissolution simultaneously, and significantly improves the cycle life of Zn anode. Because electrolyte consumption and bubble accumulation resulted from hydrogen evolution side reaction, anodes degraded ultimately when cycled in coin cells with lean electrolyte. This can be further improved by coating hydrogen evolution suppressive materials. In addition, the mechanistic understanding and design principles provide guidance to future designs of zinc and other metal anodes (e.g. Li, Na, Mg, Ca), and a path towards rechargeable Zn-air aqueous batteries and other rechargeable, high-energy and safe batteries.
A Deeply Rechargeable Zinc Anode With Pomegranate-Inspired Nanostructure for High-Energy Aqueous BatteriesAlso, some zinc battery systems using mild electrolytes, such as ZnSO4-MSO4 (M=Mn, Co), Zn(CF3SO3)2—Mn(CF3SO3), and Zn(TFSI)2—LiTFSI, in which expensive TFSI salts should be replaced with salts having lower costs, were developed to mitigate the zinc dendritic growth effectively. Nevertheless, the reversibility of a zinc anode in alkaline electrolyte is a great concern to exploit some highly rechargeable Zn-air batteries with high specific energy density (5200 Wh/kg).
To tackle the long-standing challenges of a completely rechargeable Zn anode in a limited quantity of electrolyte, in another exemplary embodiment of the present invention, the present invention comprises a ZnO pomegranate (Zn-pome) material in which the zinc oxide nanoparticles (ZnO NPs) are analogous to seeds that are individually encapsulated and held in clusters by a carbon shell diaphragm. The carbon shell coating on the nanoparticles was chosen for its porosity, stability in aqueous alkaline media, and electroconductivity.
First, multi-layered carbon acts as a conductor, protector, and ion barrier in Zn-pome to adequately constrain the migration of Zn(OH)42− (the discharge product), thus mitigating the dendrite formation and shape change of the Zn electrode. Meanwhile, species with a smaller diameter (e.g., OH and H2O) than zincate can permeate through the carbon shell.
Second, the use of nano-scale (<approximately 100 nm) primary ZnO particles avoids passivation. Once ZnO reaches a critical passivation thickness, it can no longer fully convert to Zn. The thickness of the passivation layer on the zinc foil in coin cells after complete discharging was determined by SEM. As shown in
Third, the Zn-pome has a smaller solid-electrolyte contact area than ZnO@C NPs (as shown in
The synthesis of Zn-pome is schematically illustrated in
The powder of ZnO clusters (approximately 100 mg) was dispersed in 100 mL of water in 200 mL beaker, and 1000 μL Tris buffer pH 8.5 was added into the beaker while it was stirred at 200 rpm/min The dopamine (200 mg, Aldrich) was added to the mixture, which was then stirred for 24 hours. The Zn-pome was collected by centrifugation at 1500 rpm and washed three times with distilled water. The water was subsequently removed by heating at 80° C. The final Zn-pome was carbonized at 600° C. for 1 hour with a heating rate of 5° C./min in argon atmosphere.
CharacterizationThe morphology analysis of bare ZnO, ZnO Clusters, and Zn-pome was carried out using SEM (Hitachi SU 8230). The morphology of Zn-pome and the carbon shell after etching the ZnO cluster was determined using TEM (Hitachi HT7700). The cross-sectioned images of clusters after being etched in 1M HCl were generated using FEI Nova Nanolab 200 FIB/SEM that included SEM imaging and FIB milling. The XRD pattern (Panalytical XPert PRO Alpha-1) for bare ZnO, ZnONPs@C, and Zn-pome were carried out with CuK-Alpha radiation.
The XPS was measured with AlK-Alpha (Thermo K-alpha). XPS survey spectra and high-resolution spectra of Zn2 p, O1s, and C1s were measured. The weight percentage of ZnO in Zn-pome was determined from the weight loss curves measured under air atmosphere on a thermogravimetric analysis (TGA) instrument (TA instrument, Q500) with a heating rate of 5° C./min to 850° C. The specific BET surface areas and pore size distribution were determined by physisorption (BELSORP-MAX, Microtrac BEL Japan, Inc.). The dissolved concentration of bare ZnO, ZnONPs@C, Zn-pome in 4M KOH electrolyte was measured with an ICP measurement: three samples with the same amount of active material were immersed into 4M KOH for 5 minutes, and the supernatant after centrifugation was measured. The ICP samples were filtered with 0.2 μm Acrodisc IC PES filters and diluted 100 times in ICP Matrix Solution.
Electrode PreparationApproximately 151 mg synthesized Zn-pome was gently ground in a mortar and transferred into a 4 mL vial with 0.5 g N-Methyl-2-pyrrolidone (NMP) (Aldrich), then the 1.2 g NMP solution containing PVDF (MTI, ˜10 wt % of PVDF) was added to the sample and stirred for 30 minutes. The slurry was then cast onto Sn foil (Alfa) with a Doctor's blade and dried at 80° C. for 30 minutes.
Electrochemistry2032 coin cells were assembled under ambient environment, with Zn-pome anode, Ni(OH)2 cathode obtained from commercial Zn—Ni batteries (PowerGenix), and a separator (GF 6, Whatman). The aqueous electrolyte contains 4M KOH (Aldrich), 2M K2CO3 (Aldrich) and 2M KF (Aldrich). The control cells were assembled using the same process as Zn-pome anode batteries, just with the Zn-pome anode replaced by the bare ZnO anode. The cells were charged and discharged at 1 C for comparison between bare ZnO and Zn-pome, and the performances of the 5 C rate discharge and self-discharge were investigated, respectively.
The SEM images of ZnO clusters were investigated under various magnifications (
The detailed structure of the Zn-pome was investigated using HRTEM and FIB analysis. According to TEM images (
Moreover, the coated carbon framework was stable even without the solid “seeds,” i.e., ZnO NPs, which is important for the structural stability of Zn-pome, especially when the active Zn material is mainly oxidized and dissolved after the deep discharge process.
XRD and XPS were used to characterize the crystal structure and chemical composition of Zn-pome (
Similarly, strong C1s signal and relatively weak Zn 2 p and O1s signals in the XPS survey spectrum can be observed for Zn-pome in comparison with that for ZnO NPs. Accordingly, Zn-pome is characterized as ZnO NP clusters uniformly coated with an amorphous carbon layer. The content of carbon is found to be approximately 40% in Zn-pome based on TGA in air, as shown in
To verify the ion-sieving ability of the carbon coating, the dissolution rate of ZnO in an aqueous alkaline electrolyte was investigated. Samples of ZnO NPs, ZnO@C NPs and Zn-pome containing equal amounts of zinc were immersed in 1 mL 4M KOH solutions at the same time. After a certain amount of time, the concentrations of Zn species dissolved in the solutions were analyzed by ICP. As shown in
The electrochemical performances of Zn-pome and ZnO NPs were evaluated by a full cell configuration comprising Ni(OH)2 cathode with excess capacity obtained from commercial zinc-nickel batteries. The cells were cycled at 1 C in a voltage window between 1.5 and 2.0 V in 2M KF, 2M K2CO3 and 4M KOH. It should be noted that the battery testing protocols used in this study were extremely harsh in three aspects: (1) limited electrolyte: 2032 coin cells were used with a limited amount of electrolyte (
Under such harsh testing conditions, the cells containing Zn-pome anode (Zn-pome/Ni(OH)2) exhibited remarkable capacity and cycle life, which were superior to those of ZnO NP and ZnO NPs@C anodes with Ni(OH)2 cathode, respectively.
As shown in
Other issues stem from the HER on the surface of zinc, which not only worsens efficient utilization of zinc but also leads to swelling of the cell, causing the cell to crack and the electrolyte to dry out. The loose contact in the cells inflated by hydrogen further causes abrupt capacity fading. In contrast, the capacity of Zn-pome/Ni(OH)2 is stable for 50 cycles and then gradually decreases, showing better cyclability than that of Zn NPs/Ni(OH)2. This improvement can be ascribed to the ion blocking ability of the carbon shell in the Zn-pome anode and the smaller solid-electrolyte contact area.
The improved performance of Zn-pome/Ni(OH)2 cells compared to that of Zn NPs/Ni(OH)2 is due to the ion-sieving ability of the carbon shell and secondary particle structure. The increase in charging voltage in consecutive cycling is possibly due to the accumulation of hydrogen evolved in the reduction of water. Although managing gas generation in sealed cells remains a concern, hydrogen evolution can be effectively suppressed by the adjustments of electrolyte (such as the use of water-in-salt or solid state additives).
The electrochemical performance of Zn-pome/Ni(OH)2 is also superior to that of Zn NPs/Ni(OH)2 at a higher discharge rate (5 C), as shown in
To further investigate dissolution-resistivity, coin cells were used for one cycle at 0.5 C and then rested for 24 hours before resuming cycling at 1 C. During the 24 hour resting period, Zn anodes were in the discharged state, and ZnO, the dominant species, rapidly dissolved in the electrolyte if left unprotected (
The morphology evolution of Zn-pome was investigated by SEM (
A nanoscale pomegranate-inspired hierarchical Zn anode material (Zn-pome) is fabricated via a bottom-up microemulsion approach. Each Zn-pome microsphere is around 6 μm in size and is composed of on the order of 105 ZnO nanoparticles individually encapsulated by an amorphous, microporous, and conductive carbon shell that slows down the dissolution of zincate intermediate species during cycling. The secondary structure further suppresses the zinc dissolution by decreasing the electrode-electrolyte contact area. ICP analysis confirms that Zn-pome exhibits significantly suppressed dissolution of zinc compared to ZnO NP nano-particles and ZnO@C nanoparticles.
The Zn-pome anode demonstrates remarkable capacity and cycle stability under extremely harsh testing conditions (limited electrolyte, ZnO-free electrolyte, and 100% DOD); it also retains high capacity after long-term resting in a discharged state, in which ZnO in the electrode has a massive tendency to dissolve. The success of the Zn-pome anode can be ascribed to inventive design principles that manage soluble intermediates during repeated electrochemical cycling; this is important for future designs of Zn aqueous anodes as well as other battery systems involving soluble intermediates (e.g., lithium-sulfur batteries).
Ion-Sieving Carbon Nanoshells for Deeply Rechargeable Zn-Based Aqueous BatteriesAn optimized structure to solve Zn anodes' passivation and dissolution problems simultaneously is fashioned. Specifically, the structure features (1) a sub-micrometer ZnO particle as the core, and (2) an ion-sieving carbon coating as the shell. First, unlike the bulk Zn foil which is several hundreds of micrometers thick, sub-micrometer particles will not have a passivation problem and will remain active in extended cycling. Starting from ≈100 nm ZnO nanoparticles (discharged state) rather than Zn nanoparticles (charged state) was selected because on the synthesis and scalability aspect, compared to Zn, ZnO is much easier to make into nanostructures which serves as the starting material.
On the battery performance aspect, starting from Zn to ZnO will rupture the carbon shell due to volume expansion. It is of note that nanoparticles with even smaller diameter offer no further benefit to reversibility but have much more severe dissolution concerns. The carbon shell is deposited on the ZnO nanoparticles through carbonization of a uniform polydo-pamine coating. The ability of polydopamine coatings to form a uniform shell with controllable thickness has been confirmed before. The present two-step synthesis method is relatively simple and scalable, and the carbon shell thickness is controllable by simply adjusting the dopamine mass during synthesis.
ZnO@C Synthesis100 mg commercial ZnO nanoparticles (<approximately 100 nm, Aldrich) were dispersed into 100 mL DI water followed by 10 minutes of ultrasonication, then 1 mL of Tris-buffer (pH 8.5, Alfa) and 100 (1:1), 200 (2:1) and 300 (3:1) mg of dopamine hydrochloride (Aldrich) were added and mixed for different nanoshell thickness, and then stirred for 24 hours. The fabricated polydopamine-coated ZnO nanoparticles ZnO@P were collected and washed with DI water two times in the centrifuge and dried overnight. Then the ZnO@P particles were heated in a tube furnace under Ar gas to 400° C. with a rate of 1° C./min and stayed for two hours, then to 600° C. with a rate of 5° C./min and stay for one hour.
CharacterizationThe morphology analysis of ZnO@C nanoparticles was carried out using SEM (Hitachi SU 8230) and TEM (Hitachi HT7700). The weight percentage of carbon for the sample was determined from the weight loss curves measured under ambient environment on a TGA (TA instrument, Q500) with a heating rate of 5° C./min to 850° C. The threshold ZnO@P calcination temperature was measured with TGA by heating the sample in Ar gas to 900° C. with a heating rate of 5° C./min.
The XRD pattern (Panalytical XPert PRO Alpha-1) for both bare ZnO and ZnO@C nanoparticles were carried out with CuK-Alpha radiation. The specific BET surface areas and pore size distribution were determined by physisorption (BELSORP-MAX, Microtrac BEL Japan, Inc.). The XPS was measured with AlK-Alpha (Thermo K-alpha), XPS survey spectra and high-resolution Zn 2 p, O1s, C1s spectra were measured.
The dissolved concentration of both samples in 4M KOH electrolyte was measured with an ICP measurement, the samples with the same among of active material were immersed into 4M KOH for 5 minutes, 1 day and 10 days, and the supernatant after centrifugation was measured. The ICP samples were filtered with 0.2 μm Acrodisc IC PES filters and diluted 100 times in ICP Matrix Solution.
Electrode PreparationSynthesized ZnO@C or as-received ZnO nanoparticles was mixed with carbon black (MTI) and PVDF (MTI) of an 80:10:10 ratio and grinded in a mortar, then NMP (Aldrich) of two times the mass of slurry was added to the sample and stirred in a 4 mL vial for 8 hours to ensure the slurry uniformity. The slurry was then casted onto Sn foil (Alfa) with a Doctor's blade and dried at 90° C. for 1 hour then calendared.
Electrochemistry2032 coin cells were assembled under atmosphere environment with the can at the bottom, followed by the ZnO anode, 100 μL electrolyte immersed separator, then the Ni(OH)2 cathode, spacer, spring and the cap. A commercial Ni(OH)2 electrode (PowerGenix) was used as the cathode. The separator used for battery testing was glass fiber filter (GF 6, Whatman) unless otherwise noted.
The composition of the electrolyte was KOH (4M, Aldrich) with
The voltage cutoff for GCPL was 2 V and 1.5 V for the charging and discharging processes, the cells were charged and discharged at 1 C for comparison between bare ZnO and ZnO@C nanoparticles. The mass loading of bare ZnO and ZnO@C was 1.03 mg and 0.904 mg for the comparison at low mass loading. Another set of experiments were conducted with 0.941 mg of bare ZnO and 0.98 mg of ZnO@C. The capacity for each cell was calculated with Equation 16:
Where n is the number of electrons transferred in the relevant reaction, and F is the Faraday constant.
ComputationPlanewave DFT calculations were performed within the generalized gradient approximation of Perdew, Burke, and Ernzerhof (PBE) using the Vienna ab initio Simulation Package (VASP). Projector augmented wave pseudopotentials were used for all calculations. A planewave basis set cutoff energy of 600 eV, k-point sampling at Γ, and an interionic force requirement of forces <0.01 eV/Å were used to model molecular species in a cubic box with 20 Å edge length. All ions were allowed to relax freely to convergence, and molecular species size was determined from the ionic coordinates.
The characterizations and battery performance are for the powders synthesized with a 2:1 dopamine hydrochloride to ZnO nanoparticles ratio except otherwise specified.
As noted, the pore size of the carbon nanoshell is tailored to allow hydroxide ions to pass through while blocking transport of zincate ions. During charging, the zincate intermediate is trapped inside the carbon shell and reacts with Zn within the shell, preventing deposition of Zn in another location. In contrast, the OH− by-product can diffuse out freely through the micropores in the shell due to their smaller size. During discharging, the trapped Zn oxidizes to form ZnO with the participation of OH− coming from outside the shell.
The uniform polydopamine shell is first coated onto ZnO nanoparticles by stirring the particles with dopamine hydrochloride in Tris buffer (pH 8.5) for 24 hours at room temperature in the presence of air. After carbonization at 600° C., ZnO@C nanoparticles are obtained.
The particles are of short rod-like shapes. An SEM image shows a quasi-spherical morphology of ZnO@C (
TEM images of single coated particles with different coating thickness are shown in
TEM results confirm partial ZnO loss inside the carbon shell at 700° C. and complete loss at 800° C. This phenomenon is also confirmed by the fact that 100 mg ZnO@polydopamine becomes ≈20 mg after 800° C. carbonization, and ≈70 mg after 600° C. treatment, respectively. Complete and self-supporting hollow carbon nanoshells can be obtained after etching away ZnO using HCl (
To investigate the nature of the zincate and hydroxide anion species, density functional theory (DFT) calculations discussed above were performed to study the structure and size of each species. The sizes of hydroxide ion and zincate ion, without solvation shells, are simulated to be 2.42 and 6.09 Å, respectively (
XPS results confirm the uniformity of the carbon coating. As shown in
Hydroxide species are expected to be more mobile and zincate species to be less mobile when diffusing through the nanoshell. In comparison, uncoated ZnO particles do not have pores in the same range. To directly verify the ability of the sample to prevent ZnO@C from dissolving into the alkaline electrolyte, both ZnO and ZnO@C powders are soaked in KOH (4M) for 5 minutes, 1 day, and 10 days and the dissolved Zn(OH)42 − are quantified using inductively coupled plasma atomic emission spectroscopy (ICP-AES). As shown in
To evaluate the electrochemical performance of ZnO@C nanoparticle anodes, they were paired with commercial Ni(OH)2 counter electrodes with largely excess areal capacity. 2032 coin-type batteries are used to limit the amount of electrolyte and mimic practical application conditions. A Ni(OH)2 counter electrode is used rather than an air electrode to evaluate the present anode because Ni(OH)2 has simpler electrochemistry, fewer factors influencing its battery performance, and it is compatible with sealed coin cells.
The cells are galvanostatically charged to the theoretical capacity (658.5 mAh/g(ZnO)) and fully discharged to 1.5 V at 1 C rate and 100% DOD. An upper voltage cutoff of 2 V is set to avoid electrolyte decomposition.
Noticeably, bare ZnO quickly decays to half of the initial energy storage capacity, while ZnO@C has a significantly slower decay and longer cycle life. Another set of cycling data shown in
The nitrogen doping also facilitates the conductivity of the carbon layer and charge transfer at the interface.
To compare the battery performance under harsh testing conditions reported in this work to the performance under mild testing conditions in most of the past reports, we test a ZnO@C pouch cell using electrolyte saturated with ZnO (
Another ZnO@C pouch cell using electrolyte saturated with ZnO shows a performance of ≈95% efficiency and 100% retention for 500 cycles (
In yet another exemplary embodiment of the present invention, the dissolution and passivation problems of Zn anode materials is simultaneously solved by applying an ion-sieving carbon nanoshell coating onto ZnO nanoparticles which are well below the critical passivation thickness. The carbon nanoshell is uniform and complete. The micropores successfully slow down ZnO dissolution and limit zincate ion transport, but allow hydroxide ions to pass freely, and the nanoshells' rigidity prevents anode shape change and dendrite growth.
The battery lifetime is greatly enhanced with the ZnO@C anode; the coated anode outperforms bare ZnO and Zn foil with ≈1.6 and 6 times longer cycle life in a coin cell with harsh testing conditions, respectively. The synthesis is relatively simple and scalable with a controllable nanoshell thickness.
It is to be understood that the exemplary embodiments and claims disclosed herein are not limited in their application to the details of construction and arrangement of the components set forth in the description and illustrated in the drawings. Rather, the description and the drawings provide examples of the exemplary embodiments envisioned. The exemplary embodiments and claims disclosed herein are further capable of other exemplary embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purposes of description and should not be regarded as limiting the claims.
Accordingly, those skilled in the art will appreciate that the conception upon which the application and claims are based can be readily utilized as a basis for the design of other structures, methods, and systems for carrying out the several purposes of the exemplary embodiments and claims presented in this application. It is important, therefore, that the claims be regarded as including such equivalent constructions.
Claims
1. An electrode comprising:
- anodic core elements comprising core material, the core material having a core material passivation interface size, a core material intrinsic dissolution rate, and a core material hydrogen evolution reaction (HER) rate; and
- a conformal shell coating on an outer surface of the anodic core elements forming core/shell structures;
- wherein the anodic core elements comprise a feature size smaller than the core material passivation interface size;
- wherein a dissolution rate of the core material from the core/shell structures is less than the core material intrinsic dissolution rate; and
- wherein the HER rate of the shell is less than the core material HER rate.
2. The electrode of claim 1, wherein the electrode is deeply rechargeable.
3. The electrode of claim 1, wherein the electrode has a depth of discharge (DOD) of greater than 50%.
4. The electrode of claim 1, wherein the core material is selected from the group comprising a metal, metal oxide, metal sulfide, and combinations thereof.
5. The electrode of claim 1, wherein the core material is selected from the group comprising Zn, Li, Na, Mg, Ca, ZnO, Li2O, Na2O, MgO, CaO, ZnS, Li2S, Na2S, MgS, CaS, and combinations thereof.
6. The electrode of claim 1, wherein the conformal shell coating comprises a cermet.
7. The electrode of claim 1, wherein the conformal shell coating comprises carbon.
8. The electrode of claim 6, wherein the core/shell structures have a specific discharge capacity of at least 70% of the theoretical limit of the specific discharge capacity of the core material.
9. The electrode of claim 6, wherein the electrode has a coulombic efficiency greater than about 93.5%.
10. The electrode of claim 1, wherein the anodic core/shell structures are formed by a deposition technique of layers of the conformal shell coating over a deposition cycling series; and
- wherein a morphology of the anodic core elements prior to the deposition cycling series is substantially the same as a morphology of the core/shell structures after the deposition cycling series.
11. The electrode of claim 1, wherein the anodic core/shell structures are formed by an atomic layer deposition (ALD) technique of layers of the conformal shell coating over an ALD cycling series; and
- wherein a morphology of the anodic core elements prior to the ALD cycling series is substantially the same as a morphology of the core/shell structures after the ALD cycling series.
12. The electrode of claim 1, wherein:
- the anodic core elements are nanorod structures;
- the core material comprises ZnO; and
- the conformal shell coating comprises TiNxOy.
13. The electrode of claim 12, wherein the feature size is diameter of the nanorod structures; and
- wherein the diameter is less than approximately 2 μm.
14. (canceled)
15. The electrode of claim 12, wherein the conformal shell coating has a thickness of less than 10 nm.
16. (canceled)
17. The electrode of claim 12, wherein the core/shell structures have a specific discharge capacity of over 500 mAh/g.
18. The electrode of claim 1, wherein:
- the anodic core elements are nanoparticles;
- the core material comprises ZnO; and
- the conformal shell coating comprises carbon.
19. The electrode of claim 18, wherein the conformal shell coating comprises an amorphous, microporous, and conductive carbon.
20. The electrode of claim 19, wherein an assembly of core/shell structures form Zn-pome microspheres (pomegranate-like nanoporous carbon-coated ZnO clusters).
21. The electrode of claim 20, wherein each Zn-pome microsphere has a diameter of approximately 6 μm.
22. The electrode of claim 20, wherein each Zn-pome microsphere comprises on the order of approximately 105 core/shell structures.
23.-26. (canceled)
27. The electrode of claim 20, wherein the Zn-pome microspheres have a specific discharge capacity of over 400 mAh/g.
28. (canceled)
29. The electrode of claim 18, wherein the conformal shell coating comprises an ion-sieving carbon shell.
30.-33. (canceled)
34. A rechargeable battery system comprising:
- the electrode of claim 1, wherein the anodic core/shell structures comprise a ZnO core coated with a shell layer of TiNxOy,
- an aqueous electrolyte; and
- a cathode.
35. The rechargeable battery system of claim 34, wherein one or more of:
- the rechargeable battery system is deeply rechargeable;
- the rechargeable battery system has a depth of discharge (DOD) of greater than 50%;
- each of the core/shell structures function as an electrical pathway and is electrochemically active, and the dissolution rate of Zn from the anodic core/shell structures is less than the intrinsic dissolution rate of ZnO; and
- the anodic core/shell structures comprise nanorod structures.
36.-38. (canceled)
39. The rechargeable battery system of claim 35, wherein the cathode comprises Ni(OH)2.
40. The rechargeable battery system of claim 35, wherein the anodic core/shell structures are formed by an atomic layer deposition (ALD) technique of the TiNxOy on the core over an ALD cycling series; and
- wherein a morphology of the core prior to the ALD cycling series remains substantially the same as the morphology of the core/shell structures after the ALD cycling series.
41. The rechargeable battery system of claim 40, wherein the ALD cycling series comprises at least 100 cycles.
42. The rechargeable battery system of claim 41, wherein over an electrochemical cycling series of the battery, the morphology of the core/shell structures after the electrochemical cycling series is substantially the same as the morphology of the core/shell structures prior to the electrochemical cycling series.
43. The rechargeable battery system of claim 42, wherein a mass loading of the anodic core/shell structures is greater than approximately 1.7 mg/cm2.
44. The rechargeable battery system of claim 35, wherein the core has a core specific discharge capacity;
- wherein the core/shell structures have a core/shell specific discharge capacity;
- wherein if the battery has a core electrochemical cycling series defined as the number of cycles until the core specific discharge capacity decays to 50%;
- then a core/shell electrochemical cycling series defined as the number of cycles until the core/shell specific discharge capacity decays to 50% is at least 150% longer than the core electrochemical cycling series.
45. A rechargeable battery system comprising:
- the electrode of claim 1, wherein an assembly of core/shell structures form anodic Zn-pome microspheres each comprising a pomegranate-like assembly of individual ZnO nanoparticles coated with a shell layer of carbon;
- an aqueous electrolyte; and
- a cathode.
46. The rechargeable battery system of claim 45, wherein the rechargeable battery system is deeply rechargeable.
47. The rechargeable battery system of claim 45, wherein the Zn-pome microspheres are configured with ion-sieving ability due both to the shell layer of carbon and the micro-structure of the Zn-pome microsphere; and
- wherein the dissolution rate of Zn from the Zn-pome microspheres is less than the intrinsic dissolution rate of ZnO.
48.-49. (canceled)
50. A rechargeable battery system comprising:
- the electrode of claim 1, wherein the anodic core/shell structures comprise anodic core/shell nanoparticles comprising a ZnO core coated with a shell layer of carbon;
- an aqueous electrolyte; and
- a cathode.
51. The rechargeable battery system of claim 50, wherein the rechargeable battery system is deeply rechargeable;
- wherein the conformal shell coating comprises an ion-sieving carbon shell;
- wherein the core/shell nanoparticles have a diameter less than approximately 2 μm;
- wherein the conformal shell coating has a thickness of less than approximately 30 nm; and
- wherein the cathode comprises Ni(OH)2.
52.-57. (canceled)
Type: Application
Filed: Sep 3, 2020
Publication Date: Aug 11, 2022
Inventors: Nian Liu (Atlanta, GA), Yutong Wu (Atlanta, GA), Yamin Zhang (Atlanta, GA)
Application Number: 17/639,824